Love between political theorists wasn't just a European affair. John Adams, the 2nd President of the United States, consulted his brilliant wife Abigail about practically everything he did. The couple wrote voluminous letters to each other about intellectual affairs, which they adorably signed Lysander and Diana. In addition to being a true power couple, they were also awesome parents: their son John Quincy Adams went on to become the 6th President of the United States.